Rubbers and/or elastomers are widely used in industrial applications including tires and thermoplastic polyolefins (TPOs) used in car bumpers, etc. These materials have the ability to deform reversibly when subjected to large strains. However, this advantage fast reaches a ceiling point with respect to balance in properties such as the stiffness requirements in many automotive interior and exterior applications.
Polypropylene (PP) based TPO is one the most important categories of materials that are extensively being used in interior and exterior automotive parts. TPOs can be prepared by melt blending or by in-situ polymerization. Melt blending is a fast and cost-effective method to produce a variety of toughened compositions and it allows the inexpensive addition of fillers, additives and reinforcing materials such as fibers of any nature to the matrix resin. TPOs are of lower cost and density compared for example to polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS), and therefore, more used in practice. Pure TPOs as explained herein have undesirable stiffness and henceforth are traditionally reinforced with mineral fillers, fiber or both in order to provide acceptable performance. These materials are used to improve the stiffness and other important properties such as the heat deflection temperature (HDT). Commercially available TPOs are talc filled (or other mineral fillers such as calcium carbonate) or short glass fiber reinforced or both. It is well known for those versed in the manufacturing of reinforced TPOs that inorganic fillers dramatically increase the density of the material.
An example is provided in United States patent application publication No. US20070037914A1, which discloses the use of talc to improve the flexural modulus and HDT of PP-based TPO. Another example is provided in the European patent application EP2036947A1, which describes a TPO compound reinforced with wollastonite and calcium carbonate up to 25% of total compound weight. While inclusion of these mineral fillers improves properties such as stiffness and strength, the density and toughness of the compounds is dramatically compromised. In the overall context, automakers are constantly seeking ways to reduce the weight of vehicles. In addition, it is in the interest of this industry to find sustainable bio-based materials. Therefore, such combinations of performance and sustainability must result in practical applications. Light-weight and sustainable materials in contrast to current traditional filled TPOs are a pressing need in the automotive industry and persist as a present challenge.
The urge of reducing the petroleum dependence along with the advantages offered by low cost to density ratio bio-based materials has led to the acceptance of biobased fillers in various composite applications [1]. Natural fibers and fillers have intrinsic lower density than glass fibers and mineral fillers. Henceforth, there have been a number of attempts to use natural fibers or fillers or both in PP-based compositions instead of glass fibers or mineral fillers. It is well known, however, for those versed in the art of making composites based on natural fillers or fibers that the resulting composites present intrinsic poor interphase compatibility, which induce low values of impact toughness. Other factors that limit the use of natural fibers are their hydrophilic nature as well as their low ability to withstand processing temperatures higher than 200° C. for relatively prolonged periods of time [2]. In addition, high loading of fibrous reinforcement causes property anisotropy in the final parts, which is detrimental where high geometrical precision is required [3]. Because of these limitations, most of the current polypropylene filled with natural fibers composites are produced with compression molding or needle punch techniques such as the one described in U.S. Pat. No. 6,660,201B1. There are a few works done on utilization of biochar together with wood fiber for decking and construction applications [4]. Other works on carbonized lignin and engineering plastics also have shown that inclusion of carbonized lignin can induce improvement in some of the mechanical properties of the virgin plastics, but other important properties would suffer [5]. It is important to note that in most of the scenarios the addition of carbonized material results in a noticeable reduction in impact strength of the composites.
Recently beta nucleating agents (NA) were used in order to improve impact toughness of polypropylene based TPOs [6]. While this technique improved the toughness of un-filled TPOs without hampering the other properties, addition of mineral fillers to the compound interferes with the beta NAs and would not allow them to nucleate the polypropylene efficiently. Therefore, this technique becomes inefficient with regards to filled TPOs.
The present invention discloses a route to provide balance between stiffness and toughness in toughened polyolefins. These compositions contain different loads of impact modifiers or rubbery phases as well as varying type and loads of fillers or additives or both acting in synergy with the filler or carrier resin or both while providing durability comparable to current filled compositions. More specifically, the present invention overcomes the challenges mentioned before (i.e. urge of reducing petroleum dependence, overcoming the low value of impact toughness when using natural fibers, capability of using a nucleating agent that can nucleate the PP in the presence of a filler, and so forth) by utilizing biocarbon as a filler material and fiber reinforced hybridization systems in toughened polyolefin compositions. The use of biocarbon as described herein provides valuable advantages. It is a low-cost renewable material that can be produced sustainably with a low carbon footprint. In fact, biocarbon can be produced with net negative carbon emissions. Biocarbon is thermally stable at high temperatures and can be mixed and processed with plastics without degradation to produce strong and stiff composites. In the exemplary embodiments herein disclosed, it is described how biocarbon can be used together with glass fibre or carbon fibre or both as reinforcements to achieve very high strength, stiffness and toughness without compromising the density of the composite. It is necessary to highlight that the use or weight load of the fiber reinforcement is relatively minimal compared to the total mass of the composites, resulting in high stiffness, yet keeping acceptable to very high impact strength resistance to toughness ratios. We define here “minimal” as containing less than 10 weight percent of reinforcing fiber, or more preferable less than 5 weight percent.
As disclosed herein in the exemplary embodiments the aforementioned toughened compositions present high stiffness and toughness, yet show lower density and similar durability when compared with corresponding mineral-filled TPOs currently available in the market.